Check for host key error and authentication error in Clone and Push (Multiple Branches) forms

Async load of Branches in Multiple Branches Push
Centralized message box
Merge branch 'emanuelhp/master'
Common source for invoking cache hostkey.
Translation moved.
Added CommitDialogNumberOfPreviousMessages AppSettings (default value: 4), and using it in FormCommit (replaces the hard coded value).
Reformatted code.
Added editor for CommitDialogNumberOfPreviousMessages AppSetting to GitExtensionsSettingsPage.
'AutoScroll = true' for GitExtensionsSettingsPage.
Extracted CommitDialogSettingsPage from GitExtensionsSettingsPage.
Refactoring: Removed unused GitExtensionsSettingsPage.GetPageReference().
Realigned settings controls in GitExtensionsSettingsPage + refactoring (now using Dock=Top to align the group boxes).
Updated CommitDialogSettingsPage to use a table layout manager.
Merge branch 'pr/n2046_ulrichb'
Ensure there is no more than CommitDialogNumberOfPreviousMessages messages in menu